1. Field of the Invention
The present invention generally pertains to an improved method for controlling the operating characteristics of an internal combustion engine coupled to a drive train having a continuously variable transmission or a properly spaced multi-speed transmission, and more particularly to a partial charge depletion and charge sustaining control method suitable for use with smaller battery packs.
2. Description of the Background Art
In U.S. Pat. No. 5,842,534, incorporated herein by reference, I described a charge depletion method and apparatus for operating the electric motor and small auxiliary power unit, such as an internal combustion engine, in a hybrid electric vehicle (HEV) separately or together depending upon the driving conditions. Operation of the electric motor and auxiliary power unit are coordinated so that the vehicle operates as zero emissions vehicle (ZEV) or electric car at all speeds below a cruising threshold, unless the depth of discharge of the batteries exceeds a charge threshold in which case the vehicle operates in an HEV mode. Further, the vehicle operates in an HEV mode at speeds above the cruising threshold. The batteries are depleted during operation and are not charged by the auxiliary power unit, except during emergencies in which case the batteries are only charged enough to provide a performance enhancement to the small auxiliary power unit. In operation, the vehicle speed is sensed, the level of the depth of discharge of the battery is sensed, at vehicle speeds above a threshold speed the auxiliary power unit is activated to power the vehicle and the electric motor is used to supplement the auxiliary power unit when required, at vehicle speeds below the threshold speed the auxiliary power unit is deactivated and the electric motor is used to power the vehicle, and the threshold speed is automatically and dynamically adjusted as a function of said level of the depth of discharge.
In U.S. Pat. No. 6,116,363, incorporated herein by reference, I described another charge depletion method and apparatus where operation of the electric motor and auxiliary power unit are coordinated as a function of a control policy for the auxiliary power unit based on desired least fuel consumption and/or vehicle emissions characteristics. In operation, the speed of the vehicle is sensed, the depth of discharge of the battery is sensed, at vehicle speeds above a threshold speed auxiliary power unit is activated to power the vehicle and the electric motor is used to supplement the auxiliary power unit when required, at vehicle speeds below the threshold speed the auxiliary power unit is deactivated and the electric motor is used to power the vehicle, and the threshold speed is dynamically adjusted as a function of the depth of discharge, wherein the threshold speed and adjustment of the threshold speed are a function of a control policy for the auxiliary power unit based on desired fuel consumption and/or vehicle emissions characteristics.
In my prior U.S. application Ser. No. 09/677,288 filed on Oct. 2, 2000, which is a continuation of PCT international application serial No. PCT/US99/09880 published on May 4, 2000 as International Publication No. WO 00/25417 and incorporated herein by reference, I described a control method for internal combustion engine electric hybrid vehicles that was designed to operate with a large battery pack or a high power battery pack. This approach was an improvement of the method described in my prior patent, U.S. Pat. No. 6,054,844, incorporated herein by reference, which describes a method and apparatus for controlling the power output of an internal combustion engine in a vehicle having a continuously variable transmission (CVT) or automatic transmission (AT): In these methods, a motor/generator is controlled to counteract the negative effect of the −{dot over (R)}IESE term in the dynamic equation                                           α            DS                    =                                                                      -                                      R                    ∘                                                  ⁢                                  I                  E                                ⁢                                  S                  E                                            +                                                T                  E                                ⁢                R                            -                              T                loss                            -                              T                RL                                                                    I                DS                            +                                                R                  2                                ⁢                                  I                  E                                                                    ,                                      R          ∘                =                              ⅆ            R                                ⅆ            t                              representing the engine/transmission system where αDS=acceleration of the vehicle reflected to the drive shaft,       R    =                  S        E                    S        DS              ,IE=engine inertia, IDS=vehicle inertia at the driveshaft, SE=engine speed, SDS=drive shaft speed, TE=engine torque,Tloss=torque losses, and TRL=road load torque at the driveshaft. The motor/generator, in counteracting counteract the negative effect of the −{dot over (R)}IESE in the dynamic equation, can then be used to allow the engine to operate at “wide open throttle” (WOT), or along the “Ideal Torque/Speed Operating Line” (IOL) for best efficiency and lowest emissions, or along any other predetermined operation line. In this way, the engine can be run continuously while energy flows into or out of the battery energy storage system connected to the electric motor/generator. If the battery is large enough to drive the vehicle a long distance, then the efficiency of energy into and out of the battery is high since the battery internal resistance is low. This concept is especially desirable for a charge depletion hybrid electric vehicle as described in my prior patent, U.S. Pat. No. 5,842,534 which is incorporated herein by reference, where the large battery pack is charged from stationary powerplants. With smaller battery packs, however, the efficiency of energy into and out of the battery is lower. Therefore, there is a need for a control method that is particularly suited for use with smaller batter packs.